Intermolecular Interactions between Halogen‐Substituted p‐Benzoquinones and Halide Anions: Anion‐π Complexes versus Halogen Bonding

Abstract

Intermolecular interactions between halo‐substituted p‐benzoquinones (BQ) and halide anions were examined in solution, solid‐state and/or in silico. While X‐ray crystallography revealed only halogen bonding (XB) between tetraiodo‐p‐benzoquinone (I4Q) and halides, the results of a UV‐Vis study in solutions were consistent with the formation of 1 : 1 anion‐π complexes. DFT computations showed that the anion‐π complexes of halides with most halo‐substituted BQ molecules were more stable (by 2–7 kcal/mol) than their XB analogues, but the stabilities of different complexes of I4Q were essentially the same. Thus, the structural features of the co‐crystals with I4Q were related to multicenter XB interactions between BQs and halides, thus leading to the formation of 3D networks. The observation of anion‐π complexes in solutions was attributed to their higher molar absorptivity (by more than an order of magnitude) than that of their XB analogues. Overall, the stabilities of anion‐π and XB complexes between BQs and halides were well correlated with the values of highest electrostatic potentials on the surfaces of BQ molecules when their polarizations were taken into account.

Halogen Bonding Between Anions: Association of Anion Radicals of Tetraiodo‐p‐benzoquinone with Iodide Anions

“…The yields of certain products were apparently determined by the solvent, counter‐ions, crystallization kinetics, as well as by the rates of loss of the gaseous diiodine. In particular, we reported recently that evaporation of the solutions containing mixtures of tetraiodo‐ p ‐benzoquinone, I 4 Q, and Pr 4 NI or Bu 4 NI in acetone or dichloromethane produced 3D networks formed by XB between a neutral XB donor and I − anions . Similar evaporation of the solutions containing I 4 Q and an excess of Et 4 NI produced crystals comprising 2D planes (Figure ) formed by tetraiodo‐ p ‐benzoquinone moieties linked by iodides, which were separated by layers of Et 4 N + cations.…”

“…Thus, previous crystallizations from such systems produced either BQ −. anion‐radical salts or XB or anion–π‐bonded complexes of neutral BQ molecules with iodide . The yields of certain products were apparently determined by the solvent, counter‐ions, crystallization kinetics, as well as by the rates of loss of the gaseous diiodine.…”

“…In particular, we reported recently that evaporation of the solutions containing mixtures of tetraiodo-p-benzoquinone, I 4 Q, and Pr 4 NI or Bu 4 NI in acetone or dichloromethane produced 3D networks formed by XB between a neutral XB donor and I À anions. [18] Similar evaporation of the solutions containing I 4 Q and an excess of Et 4 NI produced crystals comprising 2D planes ( Figure 1) formed by tetraiodo-p-benzoquinone moieties linked by iodides, which were separated by layers of Et 4 N + cations. Surprisingly, these crystals contain two Et 4 N + cations per one iodide and one I 4 Q.…”

Anion‐π Interaction for Molecular Recognition of Anions: Focus on Cooperativity with Hydrogen Bonding

“…However, as these structures are promising patterns for future anion receptors designs, we highlight these structures in Figure 1 and encourage the reader to see the following references for more information. [45][46][47][48][49][50][51] Figure 1 Panel of reported anion-π bond donors used alone or in combination with hydrogen bond donors.…”

“…[118] Figure 11 Some anion receptors studied by the group of Rissanen and Albrecht. 45,51,[119][120][121]54,[112][113][114][115][116][117][118] Studies on anion receptor 2 could then be extended to different anions. [58,119] In this compound, the DABCO unit anchored the anion by a C-H…anion interaction above the center of the fluorinated aromatic ring.…”